What is a "Privateer"?

The Legal Definition of a Privateer:

"Privateer", in international law, is the term applied to a privately
owned armed vessel whose owners are commissioned by a hostile nation to carry on
naval warfare. Such naval commissions or authorizations are called "Letters
of Marque". Privateering is distinguished from piracy, which is carried out
without enlistment by a government.

Privateering was abolished by the Declaration of Paris of 1856, but the
declaration was not supported by the United States, Spain, Mexico, and
Venezuela. The Hague Conference of 1907 prescribed the conditions under
which a private merchant vessel converted to war purposes has the status of
a warship. Under the U.S. Constitution, Congress has the power to issue
"letters of marque" and therefore to make use of privateers. The
practice of Privateering preceded the creation of national navies.

During
the Middle Ages, European states having few or no warships hired merchant
vessels for hostile purposes. The issuing of "letters of marque"
to ship owners or procurers, authorizing them to prey on the commerce of the
enemy, eventually came into general use. By way of compensation, privateers
were allowed to share any booty captured. Privateering was carried on during
the American Revolution and the War of 1812. Congress authorized the
president to commission Privateering in 1863 during the American Civil War,
but the power was not exercised; the Confederacy, however, engaged in
Privateering during this period. Privateering was expressly renounced by the
United States during the Spanish-American War of 1898.

At the Hague Conference of 1922-23, called to formulate the regulation of
the use of aircraft and radio in time of war, the countries then present
issued a joint declaration against the use of privateers in aerial warfare.
The report stated that because belligerent rights at sea could be exercised
only by units under the direct authority, immediate control, and
responsibility of the warring nation, belligerent rights in the air should
also be exercised only by military aircraft.